1. Field of the Invention
The present invention relates to a pulse width modulation circuit, and more particularly, to a pulse width modulation (hereinafter referred to as "PWM") circuit for forming a high density pulse width.
2. Description of the Conventional Art
A conventional PWM circuit will be described with reference to FIG. 1. As shown in FIG. 1, a counter 1 receives a signal from a regular clock pulse Z and generates a counter value X which is synchronized to clock Z. A detector 2 detects a counter value X equal to zero that is output from counter 1. A data register 3 stores a determined pulse width data value and generates a pulse width signal Y corresponding to the data value. A comparator 4 compares pulse width signal Y from data register 3 with counter value X from counter 1 to generate a certain output when the values are identical to each other. An R/S flip-flop 5 receives outputs from comparator 4 and detector 2 to generate a pulse width modulation output.
The conventional PWM circuit described above operates as follows. As shown in FIG. 1, a reference clock signal Z is counted by counter 1 so that the result is supplied to detector 2 if the result is zero, and to comparator 4 if the result equals or exceeds one.
Then, the transmitted `zero` value passes through detector 2 to generate a high signal which, in turn, is supplied to a reset terminal R of R/S flip-flop 5. The transmitted counter value X equalling or exceeding one and a pulse width value Y from data register 3 are compared in comparator 4 to provide the high signal to a set terminal S of R/S flip-flop when the compared values are identical to each other. Thus, the successive switching of R/S flip-flop 5 produces a PWM data signal. At this time, when set signal S of R/S flip-flop 5 is high, an output signal Q is high until the reset signal is received, and output signal Q is instantly changed to low once the reset signal is supplied.
Since the pulse width is modulated by the input clock frequency in the PWM circuit of the conventional technique, the pulse width cannot be flexibly adjusted, and any desired pulse width which is smaller than a minimum reference pulse width cannot be formed. Here, due to the circuitry limitation, it has been heretofore impossible to generate a pulse of high density.